1. Technical Field
The present invention relates to a printed circuit board and a method of manufacturing the printed circuit board.
2. Description of the Related Art
The processes for forming circuits on a printed circuit board, used in manufacturing electronic equipment, may entail a number of complicated processes, such as fabricating a mask, exposing to ultraviolet rays, developing, etching, stripping, cleansing, and drying.
Recently, the demands have increased for inexpensive methods of manufacturing electronic equipment, spurred by trends towards providing electronic equipment in lower costs. There has also been an increase in the demands for establishing an environment-friendly manufacturing process, such as by reducing the use of organic solvents hitherto used in large quantities in the processes for developing, etching, stripping, and cleansing, etc. Accordingly, digital manufacturing processes, such as those employing inkjet printing, are currently receiving much attention.
In general, the circuit wiring in a printed circuit board for manufacturing electronic equipment was formed by attaching copper foils over an insulation layer made of an epoxy resin composition and then forming a pattern by etching the unnecessary portions.
In the case of a package substrate intended for mounting semiconductor chips, higher levels of thermal resistance and reliability may be required, compared to a substrate for a regular printed circuit board. Thus, the substrate was manufactured using an insulation layer made from an epoxy composition, which has a high glass transition temperature, or using a BT resin containing a bismaleimide triazine (BT) compound for the interlayer insulation material.
However, thermosetting resins having high thermal resistance, such as BT resin, may provide low adhesion to metals, such as copper, forming the conductive layer. As such, delamination may occur between the insulation layer and the metal wiring layer while performing reliability evaluation procedures such as thermal impact tests.
A method of forming a thin layer of adhesive between the insulation layer and the copper foil was proposed to resolve this problem, but because of the moisture absorption by the adhesive layer formed between the insulation layer and the copper foil, the desired levels of adhesive strength and thermal resistance may not be obtained.
Also, in accordance with the trends of decreasing costs in current electronic equipment, there is an increasing demand for low-cost manufacturing processes, and there have been numerous attempts to introduce digital manufacturing processes, such as inkjet processes, to processes for forming circuit wiring in a printed circuit board.
In cases where the circuit wiring for a printed circuit board is formed using an inkjet process, the previous processes for fabricating a mask, exposing, developing, etching, stripping, and cleansing can be substituted by the inkjet printing and curing processes, allowing vast savings in manufacturing costs.
Moreover, the large quantities of organic solvents and organic waste involved in wet processes can be avoided, whereby a more environment-friendly manufacturing process may be established.
However, when manufacturing a thermally resistant package substrate using inkjet processes, the circuit wiring may not be formed with high reliability, due to the low adhesive strength between the BT resin and the nanometal ink printed on the BT resin.
Attempts have been made to resolve this problem by laminating a thin adhesive layer over the BT resin and forming the wiring by inkjet printing over the adhesive layer. However, the different rates of contraction and expansion between the metal and adhesive layers can lead to cracking in the metal wiring during the curing of the nanometal, and thus such attempts may not be applied to actual manufacturing processes.
Thus, in order to form wiring lines on a thermosetting resin high in thermal resistance using a digital manufacturing process such as an inkjet printing process, sufficient adhesive strength is needed between the thermally resistant substrate material, such as BT resin, and the printed nanometal ink. Furthermore, there is also a need for a technique that allows the forming of fine-line wiring to implement the high level of integration in a package substrate.